diff --git a/my/demo.py b/my/demo.py
index 2df9d67..5fd8ea8 100644
--- a/my/demo.py
+++ b/my/demo.py
@@ -2,23 +2,42 @@
 Just a demo module for testing and documentation purposes
 '''
 
-from .core import Paths
+from .core import Paths, PathIsh
 
+from typing import Optional
 from datetime import tzinfo
 import pytz
 
 from my.config import demo as user_config
 from dataclasses import dataclass
 
+
 @dataclass
 class demo(user_config):
     data_path: Paths
     username: str
     timezone: tzinfo = pytz.utc
 
+    external: Optional[PathIsh] = None
+
+    @property
+    def external_module(self):
+        rpath = self.external
+        if rpath is not None:
+            from .cfg import set_repo
+            set_repo('external', rpath)
+
+        import my.config.repos.external as m # type: ignore
+        return m
+
+
 from .core import make_config
 config = make_config(demo)
 
+# TODO not sure about type checking?
+external = config.external_module
+
+
 from pathlib import Path
 from typing import Sequence, Iterable
 from datetime import datetime
@@ -46,6 +65,6 @@ def items() -> Iterable[Item]:
         for raw in j:
             yield Item(
                 username=config.username,
-                raw=raw,
+                raw=external.identity(raw),
                 dt=dt,
             )
diff --git a/tests/demo.py b/tests/demo.py
index 4dfae6d..280eab2 100644
--- a/tests/demo.py
+++ b/tests/demo.py
@@ -11,6 +11,7 @@ def test_dynamic_config_1(tmp_path: Path) -> None:
     class user_config:
         username  = 'user'
         data_path = f'{tmp_path}/*.json'
+        external  = f'{tmp_path}/external'
     my.config.demo = user_config # type: ignore[misc, assignment]
 
     from my.demo import items
@@ -29,6 +30,7 @@ def test_dynamic_config_2(tmp_path: Path) -> None:
     class user_config:
         username  = 'user2'
         data_path = f'{tmp_path}/*.json'
+        external  = f'{tmp_path}/external'
     my.config.demo = user_config # type: ignore[misc, assignment]
 
     from my.demo import items
@@ -75,6 +77,7 @@ def test_attribute_handling(tmp_path: Path) -> None:
 
         username = 'UUU'
         data_path = f'{tmp_path}/*.json'
+        external  = f'{tmp_path}/external'
 
 
     my.config.demo = user_config # type: ignore[misc, assignment]
@@ -99,4 +102,10 @@ def prepare(tmp_path: Path):
     {"key2": 2}
 ]
 ''')
+    ext = tmp_path / 'external'
+    ext.mkdir()
+    (ext / '__init__.py').write_text('identity = lambda x: x')
     yield
+    ex = 'my.config.repos.external'
+    if ex in sys.modules:
+        del sys.modules[ex]